RBC Kits HM-16 Pou du Ciel (Flying Flea)

The purpose of this thread is to describe my build and modifications to the RBC Kits HM-16 Pou du Ciel (Flying Flea) kit. Each of the following 10 posts will describe a mod or construction aspect. I am doing this to keep all of the mods at the beginning of the thread and keep them from getting buried.

There are not any US dealers for RBC Kits that I know of. Warbirds-RC.com used to be the US dealer but their website has not been working for a couple of years and I do not know what has happened to them.

If you have another US source for this kit, let me know. Any new information would be welcome.

Fuselage Modifications

1. Wing Strut Alignment: Use a jig system to align the wing struts during assembly. Add the struts when the fuselage is built up to the point where there is just a flat surface where the cowl formers and motor mount will be glued. This will be used as the surface that you mount the wing pivot wire parallel to and perpendicular to the model centerline. On the wing pivot wire, make sure you put the pieces of tubing on the wire before bending the ends.

2. Relocate Rudder Servo: Move the rudder servo from under the rear wing to the back of the cockpit. If you have a servo problem with the plans location, you will have to remove the rudder assembly and rear wing to get at it. Also use an HS-81 or similar servo because the HS-55 I used stripped its gears under the load of a minor prang. I would use HS-81s or 82s for both the rudder and front wing pivot.

3. Brushless Outrunner Motor Mount: Build a motor mount that maintains the kit propeller position and downthrust angle for your motor. Mine is a firewall mount for an Axi 2208-34. The original kit motor mount was for a Speed 400 brushed can motor.

Images

4. Cowl: I didnít like the kitís zig-zag cowl to fuselage break line so I simplified it and added a couple pair of rare earth magnets for retention.

The model is covered with silver "Litespan" which is like a heat shrinkable silkspan and does not have any adhesive. I had to brush on a coat of Coverite "Balsarite" heat activated adhesive on all of the areas to be covered and under any covering to covering seams. It is not the easiest material to work with and doesn't like going over compound curves. I chose it because of its irregular weathered silver appearance.

I mounted him on a .375" high balsa block to get his head height in the cockpit correct and stuck the block to the cockpit sill with double sided sticky tape so I can easily remove him to get at the servos.

Images

Wing Modifications

1. Reinforce Wingtips: Laminate or add carbon to the wingtips. The kit parts span a large distance and will break easily without reinforcement in the form of laminating them or adding carbon fiber sheet material on one side.

2. Modify C1: Increase the length of the "C1" plywood wing horn so it grabs at least a quarter inch of wood and put a couple of small balsa blocks on either side of the slot inside the wing. The kit part is only glued to the one layer of wing sheeting and could be easily broken off.

3. Wing Pivot Wire and Linkage: Bury the wing pivot wire flush or inside the bottom of the wing. You could build a grooved landing gear block into the bottom of the wing and retain the wire with landing gear straps to make the wing removeable. I didn’t do this on this model but would do it for appearance and functional reasons if I built another. The way the kit says to do it leaves that wire exposed below the wing.

I left the two "C2" pieces and wing pivot horn off the wing until after covering the bottom surface. After covering, I cut through the covering to open up the mounting holes and glued them in with 5 minute epoxy. 5 minute epoxy gives you some time to reposition the pieces before the glue kicks off and doesn't make the brittle joint that CA makes. I also lengthened the C2 legs and wing horn for more gluing area inside the wing.

Rudder Modifications

1. Rudder Hinging System: I replaced the orange plastic tube with a hole drilled in it and screws in the ends with a short piece of 3/32Ē brass tubing with a short piece of 1/16Ē tubing soldered to it at the center for the rudder rod. My rudder supports have "L" bends that are wrapped with tape and glued into the ends of the brass piece.

Pilots Notes

It is balanced at the plans CG by sticking a couple of pins into the fuselage sides. Make sure that the forward wing is set at neutral per the plans with the trailing edge set at 2mm higher than the leading edge. This can be measured from the flat fuselage top in front of and behind the top deck.
Test flights are best done by hand launch over high grass.

It is powered with an AXI 2208-34 with an APC 8x3.5 prop, a Turnigy Plush 12 amp ESC, and a 3S 700 lipo pack. Any outrunner of similar performance and much lower cost would be okay.

This is overpowering it and full throttle can cause it to tuck under, apparently caused by the accelerated flow over the rear wing. I can avoid the full power tuck by holding in up wing and smoothly going to full throttle. It cruises at half throttle. It will do a Lomecevak if I let off full up wing at full throttle.

Hello Richard,
Congratulations on posting such a very nice set of pictures and information on the dreaded HM16. I have the full size drawings for this aircraft plus some Mignet black and white home movies from the 30,s. Its interesting to note this version flew best in turns due to the fact the rudder is sitting high on top of the rear fuselage deck.The conventional HM293 and the HM14 skids around turns.But not the HM16.I built a modified full size version of this aircraft and test flew it. It would be one of the most difficult aeroplanes I have ever flown. The airfoils mignet 34013 and the NACA 23112 have to be set at plus 1 deg on a full size verson as you will get immediate nose over. These airfoils have no negative angle of attack lift capabilities, and so all turns to custard when you get near zero angle of attack.. However I found a cuffed naca modified 63 series, with the mean camber line pusher right forward , forming a cuff. This is an airfoil that will work down into say minus 3 deg angle of attack you have to have. I would be really interested in hearing more about your flight testing. I didn't fly my full size version into extremes as the results are mostly fatal. From my research the Flea suffers from front wing stalling and I love your comment about the fact that it noses over with two much power applied. That happens the same way in the full size version. Go to fast,I mean more then 75 m.p.h, hit some turbulence and the front wing stalls and your in a deadly nose dive. Mignet if you watch his 1930 movies NEVER lowered the nose on approach he knew better. The rear wing Cosendy flap is very effective on approaches. Always put out 20 deg , that way you stop that back wing from generating to much lift. You might like to try a fix for all of this like the Gyro people did. Install a balsa horiziontal stablizer half way up the rudder swept back a little about 14% of the rear wing area, and you will find the Flea dive problems all go away. Everything flying needs a stablizer, even a flying wing which ahs a built in one. You dont see birds flying around with no feather in their bumb! The modern full size Flea builders dreamers just fly there ultralight fleas at such a slow speed they never get caught to much in the nose over problem. However a chap wrote to me not so long ago who built a very nice flew with low H.P. and he ran into nose over problems at 60 m.p.h. He has had 3 nose over and by good luck or good managment or the grace of God managed to fly out of them.
He aslo says he never lowers the nose on approach. A chap I knew had a radio quarter scale Flea and he found that it being heavier then yours, if you put it into a dive it goes right off its head and tumbles like a drunk duck.
thanks
mig

Mig,
I have read warnings about the danger of control issues with the HM-16 design on at least one of the Flea websites. My feeling about flight testing is that I would always rather have issues resolved in model testing than with myself or a person in a real aircraft. The consequences of model testing are negligible compared to full scale accidents. I am not a full scale pilot but almost always accept full scale rides when offered. Last year, a friend tried to arrange a ride for me in a Balerit he used to own, but the new owner was out of town when I was there. That would have been my first full scale Flea flight.

The HM-16 was not my first choice for a Flea model, but it was the only available kit that was a "real" Flea: It has a pivoting front wing for pitch control and a rudder for yaw. There is a kit of an HM-14, but it has a fixed front wing with an elevator on the rear wing. Another kit I have of an HM-293 is the same way, something that looks like a Flea but is configured as a close coupled conventional airplane.

Probably the next thing I will do is progressively remove motor downthrust and see how that affects the high throttle diving.

Photos Added

Look at my avatar
I designed the thing for RBCkits quite some time ago, in the days before outrunners and micro servo's like the HS-55.
And with the space required for an 8-cell 500 mAh NiMh pack there simply was not enough space in the cockpit for a receiver and a servo. I thought my Simprop Pico Rx was small, but when I look at today's 2.4 GHz units.....